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IC 9077 



Bureau of Mines Information Circular/1986 



Dust Control on Longwall Shearers 
Using Water-Jet-Assisted Cutting 

By C. D. Taylor, P. D. Kovscek, and E. D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9077 



Dust Control on Longwall Shearers 
Using Water-Jet-Assisted Cutting 

By C. D. Taylor, P. D. Kovscek, and E. D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Model, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



/ 








Library of Congress Cataloging in Publication Data; 



Taylor, Charles D. (Charles Darrell), 1946- 

Dust control on longwall shearers using water-jet-assisted cutting, 

(Information circular ; 9077) 

Bibliography: p. 8-9. 

Supt. of Docs, no.: I 28.27: 9077. 

1, Coal mines and mining— Dust control. 2. Longwall mining. 3. 
Water-jet. I. Kovscek, P. D. (Paul D.). II. Thimons, Edward D. III. 
Title, IV. Series: Information circular (United States. Bureau of 
Mines) : 9077. 



TN295.U4 [TN312] 622s [622'. 334] 86-600037 



CONTENTS 

Page 

Abs tract 1 

Introduction 2 

Test facility 2 

Test procedure 3 

Spray sys terns 3 

Dust sampling procedures 4 

Dust sampling results 6 

Discussion 6 

Conclusions 8 

Future recommendations 8 

References 8 

ILLUSTRATIONS 

1 . Bureau of Mines longwall shearer 3 

2. Locations of test cuts and water pressures used 4 

3 . Nozzle design and bit configuration 4 

4. Locations of sampling Instrviments on longwall shearer 5 

5. Plastic tubing used for Interior sampling location 5 

6. Fluid horsepower versus dust level 6 

TABLE 

1. Test conditions and sampling results 4 





UNIT OF MEASURE ABBREVIATIONS USED 


IN 


THIS REPORT 


ft 


foot 


in 




inch 


f t/mln 


foot per minute 


mg/m^ 




milligram per cubic meter 


ft2 


square foot 


mm 




millimeter 


ftVmin 


cubic foot per minute 


pet 




percent 


gal/min 


gallon per minute 


psi 




pound per square inch 


hp 


horsepower 


r/min 




revolution per minute 



DUST CONTROL ON LONGWALL SHEARERS USING WATER-JET-ASSISTED CUTTING 

By C. D. Taylor, ^ P. D. Kovscek,^ and E. D. Thimons^ 



ABSTRACT 

The Bureau of Mines equipped a longwall shearer with a water- jet- 
assisted cutting system and measured dust levels during the cutting of a 
simulated coal block. The block was cut dry, at a conventional water 
spray pressure of 190 psi, and with water-jet-assisted cutting pressures 
ranging from 1,000 to 6,000 psi. At water pressures of 3,000 psi and 
higher, dust concentrations were reduced by as much as 85 pet via water- 
jet-assisted cutting in comparison with conventional water sprays. This 
reduction was achieved without any increase in the water flow rate. 



^Industrial hygienist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
^Project engineer, Boeing Services International, Pittsburgh, PA. 
^Supervisory physical scientist, Pittsburgh Research Center. 



INTRODUCTION 



Large quantities of respirable dust are 
generated by the cutting action of a 
longwall shearer. All longwall sections 
use sprayed water as a dust control tech- 
nique. Generally, spray nozzles are 
mounted on the body of the shearer and 
directed toward the cutting drum. These 
sprays remove part of the airborne dust 
by impacting the dust particles with wa- 
ter droplets. The efficiency of airborne 
dust removal by impaction is improved by 
increasing the quantity and pressure of 
the water supplied. The most effective 
use of water for dust control results 
from adding moisture to the generated 
dust particles before they become air- 
borne. This requires wetting the dust as 
close as practical to its point of ori- 
gin. For a longwall shearer, this is the 
point where the bit strikes the coal. 

All U.S. longwall shearers are equipped 
with a water spray system that directs 
water through the cutting drum. The wa- 
ter passes from the drxjm to spray noz- 
zles, usually located in front of each 
bit, which direct water to the bit tip. 
For these conventional spray systems, the 
water pressure at the nozzle is typically 
100 to 200 psi. 

Techniques for using high-pressure wa- 
ter jets to assist the cutting of rock 
have been evaluated by the Bureau of 
Mines and others (l).*^ For this report a 



water jet is defined as a high-pressure 
solid stream of water that is directed 
to a point within 5 mm of the bit tip. 
The coherent stream, achieved by using a 
specially designed spray nozzle, is nec- 
essary for maximum transfer of energy be- 
tween the nozzle orifice and rock sur- 
face. Use of high-pressure water jets to 
assist a mechanical drag bit is known as 
water-jet-assisted cutting. Laboratory 
test results have shown that when cutting 
at shallow depths, forces on a drag bit 
are reduced if a high-pressure water jet 
is directed toward the bit tip (2^) . To 
date no underground studies have docu- 
mented these force reductions, but use of 
roadheaders equipped with water jets has 
demonstrated improved cutting efficiency 
(3). 

In addition to improved cutting effi- 
ciency with water-jet-assisted cutting, 
the quantity of dust generated was noted 
as also being reduced. A dust sampling 
plan was designed to determine the 
relationship between water usage and the 
quantity of dust generated by the cut- 
ting action of a longwall shearer drum 
equipped for water-jet-assisted cutting. 
This report describes testing performed 
to evaluate the effectiveness of high- 
pressure versus conventional-pressure wa- 
ter sprays for dust control on a longwall 
shearer. 



TEST FACILITY 



Testing to determine the effects of wa- 
ter usage on dust levels was conducted 
using a 60-ft-long by 6-ft-high coalcrete 
block, composed of coal, fly ash, and 
concrete, to simulate a longwall face. 
Because of its higher silica content, 
coalcrete is more abrasive than coal; 
however, when using conventional drag 
bits, its cutting properties are similar. 
Overall the simulated coal face was homo- 
geneous. A longwall panline, adjacent to 



the coalcrete block, provided continuous 
removal of the coalcrete as it was cut. 

The shearer used to cut the coalcrete 
was a Joy 1-LSl^ double-drum machine 
(fig. 1). For all tests, only the lead 
drum was used for cutting; the trailing 
drum was positioned so that it moved 
within the cut made by the lead drum. 
The lead drum diameter (bit tip to bit 
tip) was 54 in, and the drum width was 
28 in. During the tests, web width 



'^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



^Reference to specific products does 
not imply endorsement by the Bureau of 
Mines . 




FIGURE 1. - Bureau of Mines longwall shearer. 



(thickness of cut) varied from 25 to 29 
in. The machine tram rate was maintained 
at approximately 5 ft/min. Drum rotation 



speed was 46 r/min (bit tip speed = 650 
ft/min) . Radial attack bits were used. 



TEST PROCEDURE 



During testing, three passes were made 
across the coalcrete block. Figure 2 
diagrams these passes, showing the rela- 
tive locations of each cut and the water 
pressures used. Dust data were analyzed 
for the sections of each pass indicated 
on figure 2. Each pass began with a 
sump cut , which allowed the face to be 
squared, prior to the first test cut. 

For the first pass , the face was 
marked off into 6-ft-long segments. Each 



segment was cut while maintaining the wa- 
ter pressure shown in figure 2. Water 
pressure of 6,000 psi was used to cut 35 
ft during the second pass; 35 ft of the 
third pass was cut using conventional- 
type spray nozzles with a water pressure 
of 190 psi. The final 15 ft of the third 
pass was cut without water sprays to pro- 
vide information for comparison of dry 
cutting with conventional wet cutting and 
cutting with high-pressure sprays. 



SPRAY SYSTEMS 



There were 32 spray nozzles on the lead 
drum. With both high-pressure and con- 
ventional spray systems , water was 



supplied only to the lead drum. For the 
high-pressure and conventional— pressure 
tests, spray nozzles, having 0.024- and 



60 ft H 



Dry cut 
15 ft 



No data 



No data 



190 psi, 35ft 



6,000 psi, 35 ft 



1,000 
psi 
6 ft 



2,000 
psi 
6 ft 



3,000 
psi 
6 ft 



7:!;77?':?Z?^5^^^^?J7fe^5^5^77TO'7?^773te7;!^:57Xte 



4,000 
psi 
6 ft 



5,000 
psi 
6fr 



6,000 
psi 
6 ft 



Sump' I 
cut 1 Thi^C 
10 ft """ 



Sump 
cut 
10 ft 



Sump 
cut 
10 ft 



Second 
poss 



-Cutting direction 



FIGURE 2. - Locations of test cuts and water 
pressures used. 

0.071-in orifices, respectively, were lo- 
cated in front of each bit, approximately 
4.0 in from the bit tip. The water-jet 
nozzles were made from stainless steel, 
3/8-in-diam hexagonal socket head screws, 
which were machined down to an internal 
13° Leach and Walker configuration. (See 
figure 3.) Brass nozzles of similar de- 
sign (13° taper) were used for the con- 
ventional sprays. Each nozzle delivered 
a solid stream of water to a location 1 
to 3 mm in front of the bit tip. Flow 
rates for nozzles operating at the pres- 
sures tested are given in table 1. 

The water supply lines to the cutting 
drum were flushed frequently, and 10-ym 




Enlarged view 
of nozzle 



FIGURE 3. - Nozzle design and bit configuration. 

filters were placed in line to reduce 
the possibility of nozzle blockage. The 
high-pressure water was supplied by a 
150-hp triplex pump with a capacity of 
50 gal/min at 6,000 psi. 



DUST SAMPLING PROCEDURES 



The cutting action of the Bureau 
shearer cutting in coalcrete was similar 
to that of a shearer cutting coal on an 
underground longwall face. However, the 
airflow pattern on an underground long- 
wall face, which has a significant ef- 
fect on the transport characteristics of 



airborne dust, could not be simulated 
during testing. Moreover, the amount of 
dust generated while cutting coalcrete 
versus coal would not be the same, due to 
physical differences in the two mate- 
rials. No attempt was made, therefore, 
to relate dust levels measured during 



TABLE 1. - Test conditions and sampling results 





Flow rate, 
gal/rain 


Fluid 
horsepower^ 


Dust concentration, mg/m^ 


Dust 


Pressure, psi 


Exterior 


Interior 


Average 


reduction, 
pet 


High-pressure: ^ 

6,000 

5,000 

4,000 

3,000 

2,000 


1.26 

1.15 

1.03 

.90 

.75 

.54 

.90 



141.1 
107.4 
76.9 
50.4 
28.0 
10.1 

3.2 

.0 


10.2 
10.9 
12.0 
11.6 
28.0 
92.4 

119.0 
102.0 


33.4 
23.1 
31.7 
34.8 
52.5 
121.2 

103.9 
223.0 


21.8 
17.0 
21.9 
23.2 
40.3 
106.8 

111.5 
162.5 


80.4 
84.8 
80.4 
79.2 
63.9 


1,000 

Conventional: ^ 

190 


4.2 
.0 


Dry cutting. ..... 


-31.4 



^Calculated for 32 sprays. 20.024-in orifice. 3o.071-in orifice. 



testing to those that would be measured 
during an actual underground mining 
operation, 

Dorr-Oliver lO-mm nylon cyclones were 
used at each sampling location to elimi- 
nate all but airborne respirable dust. 
Two "exterior" cyclones were hung about 
72 in from the cutting drum at approxi- 
mately the same height as the top of the 
cut (fig. 4). The cyclone inlets were 
positioned away from the drum to reduce 
the chance of water droplets entering the 
cyclones. Two "interior" cyclones were 




KEY 

R RAM-I dust monitor 



FIGURE 4. - Locations of sampling instruments on 
longwall shearer. 



placed inside a wooden dust sampling box 
on top of the shearer (fig. 4) . The cen- 
ter of the box had a cross-sectional area 
of 1 f t^ . A centrifugal fan mounted on 
the sampling box pulled 80 ft^/min of air 
into the sampling box through 2-1/2-in- 
diam PVC plastic tubing. The ends of the 
box were tapered to reduce sampling error 
due to airflow turbulence. The inlet for 
this sampling tubing was located approxi- 
mately 24 in from the bottom of the lead 
drum (fig. 5) . Therefore the exterior 
and interior cyclones sampled dust levels 
72 and 24 in, respectively, from the lead 
drum. 

Interior and exterior cyclones were at- 
tached by 60-in lengths of Tygon plas- 
tic tubing to real-time aerosol dust mon- 
itors (GCA RAM I's), which continuously 
monitored dust levels. The analog out- 
put from each monitor, which is propor- 
tional to the dust level, was recorded by 
a Sol tec strip-chart recorder. For each 
test, the area under the recorded curve 
was measured using a compensating polar 




FIGURE 5. - Plastic tubing used for interior sampling location. 



planimeter. The length of the baseline 
under each curve was proportional to the 
duration of the test. Each area was di- 
vided by the length of the baseline to 
obtain an average dust concentration for 
the time of testing. 

To reduce variation in sampling re- 
sults, test conditions other than wa- 
ter pressure were reproduced for each 
test. Static pressure within the box was 



carefully monitored to determine if there 
were any constrictions in the airflow 
path or any changes in fan operation. 
For each test the same monitoring instru- 
ments (RAM I's) were used at each loca- 
tion. Monitor performance was checked 
before each test by verifying that in- 
strxmient airflow was correct and that the 
digital readout gave the calibrated value 
for the reference scatter. 



DUST SAMPLING RESULTS 



Table 1 shows the water pressure and 
flow rates used and the resulting dust 
levels at both sampling locations, as 
well as the average dust levels for both 
locations. The final column shows the 
dust reductions (versus conventional op- 
eration) for each water pressure and 
flow. At 3,000 psi water pressure the 



dust levels were 79.2 pet less than when 
using conventional sprays. The dust re- 
duction at 3,000 psi was achieved with a 
water flow rate no greater than required 
for the conventional spray pressure of 
190 psi. Raising the pressure further 
from 3,000 to 6,000 psi resulted in only 
small additional dust reductions. 



DISCUSSION 



The data in table 1 showed that the 
higher water pressures and flow rates re- 
quired for water-jet-assisted cutting 
were effective in reducing levels of air- 
borne dust. Increasing either water flow 
or pressure increased the amount of fluid 
energy that was supplied to the location 
being cut. During a prior study where 
water-jet-assisted cutting was used with 
a roadheader, energy supplied by the wa- 
ter jets enabled the roadheader to cut 
hard rock that could not be cut when 



120 



100 



80 



^ 60 

UJ 



^ 40 
o 



20 



1 190 psi 
• 1,000 psi 



\ 2,000 psi 



1,000 psi _^^^ 

'3,000 psi ^^-^^ -^ 5,000 psi 



6,000 

• psi - 



" 20 40 60 80 90 120 140 150 

FLUID HORSEPOWER, hp 

FIGURE 6. - Fluid horsepower versus dust level. 



operating dry (_3) . A part of the energy 
used reduced airbrorne dust. 

During these tests the tram rate and 
depth of cut were maintained relatively 
constant. Therefore the specific energy 
supplied by the sprays can be directly 
related to the fluid horsepower. The 
quantity, P x V/1714, can be used to cal- 
culate fluid horsepower, with P being the 
pressure (psi) and V the volume (gal/ 
mln) , In figure 6, fluid horsepower for 
the seven different water pressures 
tested has been plotted versus resulting 
dust levels. The data points have a cor- 
relation coefficient of 0.90 for the 
power curve (y = ax'') shown. These data 
do not indicate whether increased flow or 
increased pressure is more important in 
causing changes in the dust level. There 
is probably a combined effect of pressure 
and flow, depending on the range of oper- 
ating conditions. 

Variations in dust concentrations, seen 
in table 1, can be attributed to various 
causes. When operating dry, dust levels 
at the two sampling locations varied pri- 
marily with respect to their distance 
from the dust source. Dust measured at 
the interior and exterior sampling loca- 
tions was drawn from areas 24 and 72 in. 



respectively, from the cutting drum. 
Therefore, dust levels were higher at the 
interior sampling location. 

When sprayed water is applied during 
a coal cutting operation, changes in 
airborne dust levels are primarily due to 
one or more of the following: 

• Airborne capture of coal dust 
particles. 

• Wetting of coal dust before it be- 
comes airborne. 

• Entrainment of dust particles caused 
by spray-induced airflow. 

The contribution jf each to dust suppres- 
sion varies with the pressure and flow 
used. 

At 190 psi the average dust concentra- 
tion decreased mainly as a result of wet- 
ting the coal surface. The flow rate 
through each nozzle at 190 psi was 0.90 
gal/min. However, underground and labo- 
ratory tests by the Bureau have shown 
that, in addition to wetting, water 
sprays can cause airflow turbulence that 
can have a significant effect on dust 
levels measured in the vicinity of a 
longwall shearer (4^) . If water spray 
nozzles mounted on the shearer body are 
not properly oriented, the resulting air- 
flow can carry dust to the shearer oper- 
ator's position. Although only drum- 
mounted sprays were used during these 
tests, in tests where the web width was 
less than the drum width, the sprays 
nearest the shearer body sprayed outside 
the coalcrete block. At 190 psi, these 
unshielded sprays created air turbulence 
that moved dust toward the exterior sam- 
pling location, resulting in slightly 
higher dust levels there than when oper- 
ating dry. 

Increasing the water pressure from 190 
to 1,000 psi did not significantly change 
dust levels at either sampling location. 
Although the pressure increased, flow 
rate at 190 psi was greater than at 1,000 
psi (0.90 vs 0.54), owing to the differ- 
ence in nozzle orifice sizes. The total 
horsepower supplied by the sprays oper- 
ating at 190 and 1,000 psi was 3.2 and 
10.1, respectively. However, the added 
energy was not sufficient to significant- 
ly affect either wetting of the coal or 
airborne particle capture. 



Dust levels were reduced 78 pet when 
the pressure was raised from 1,000 to 
3,000 psi. The additional fluid horse- 
power supplied by the sprays operating 
at 3,000 psi resulted in improved dust 
control. Higher pressure resulted in in- 
creased flow, which improved wetting. 
Higher water pressures may have contrib- 
uted to further dust reductions for the 
following reasons: 

1. Water directed at the coal at high 
pressure penetrates a short distance into 
the coal surface (2), traveling along 
natural fracture planes in the coal and 
wetting the generated dust before it is 
exposed to the ambient airflow. 

2. The dominant effect of the jets on 
the rock fracture process is to flush 
chips and rock debris from the region 
ahead of the bit (2^) . These particles 
are wetted by the jet before being re- 
moved from the face. 

3. Material cut by the longwall drxim 
"circulates" for a short time between un- 
cut coalcrete and the drum vanes before 
the screw action of the vanes pulled it 
onto the panline. Water from the water 
jets penetrates the cut material more 
quickly and mixes more thoroughly as the 
material circulates. This results in a 
more uniformly moist mined material. 

At pressures above 1,000 psi, airborne 
dust capture may have been a factor in 
reducing the airborne dust. Studies, 
such as those of Tomb (_5 ) , have shown 
that capture of airborne dust by water 
droplets increases with increased water 
flow and pressure. Minimum pressures are 
necessary before the effects of the cap- 
ture become significant. Airborne dust 
capture is not effective unless the dust 
can be confined for a short time within a 
closed space. During cutting with the 
shearer, small water droplets within the 
kerf may strike and remove a portion of 
the dust that becomes airborne in this 
space. A British study (6^) conducted on 
an operating longwall section suggests 
that the effectiveness of the high- 
pressure water may be due to better pene- 
tration of the material being cut or to 
atomization of the water stream into 
fast-moving fine droplets. It is not 
possible to determine from the data 



collected if the spray within the kerf 
affected dust levels more by improved 
wetting or by airborne capture. 

There was only a small decrease in dust 
as the water pressure was raised from 
3,000 to 6,000 psi. This was probably 
because the section of coalcrete cut at 



3,000 psi was thoroughly wetted by the 
quantity of water applied at this pres- 
sure. The additional water supplied at 
the higher pressures could not be ab- 
sorbed. Any additional dust reductions 
due to increased pressure were minimal. 



CONCLUSIONS 



The results of this study indicate that 
use of water-jet-assisted cutting can 
significantly reduce airborne dust gener- 
ated by a longwall shearer. Water-jet- 
assisted cutting is characterized by 
increased water flow rate and water pres- 
sure, and by spray-induced airflow turbu- 
lence. Varying these operating condi- 
tions had the following effects on dust 
levels: 

1. At 190 psi. — Although wetting of 
some dust occurred within the area being 
cut by the shearer drum, spray-induced 
airflow increased dust levels at the ex- 
terior sampling location. 

2. From 190 to 1,000 psi. —Water flow 
decreased and fluid horsepower increased. 
The added fluid horsepower was not suffi- 
cient to offset the effect of reduced 
wetting. 



3. From 1,000 to 3,000 psi. —Higher 
pressure resulted in more efficient wet- 
ting of cut and uncut material within the 
area cut by the shearer. Increased wet- 
ting occurred as flow rates increased. 
Less dust escaped from the area being 
cut, as a result of increased wetting and 
possibly of improved airborne capture. 
Therefore, airflow turbulence became less 
of a factor affecting dust levels. Dust 
levels were reduced by approximately 
78 pet. 

4. From 3,000 to 6,000 psi.— Water 
quantity at 3,000 psi provided maximum 
effective wetting for the amount of mate- 
rial being cut. Increased water pressure 
did not improve wetting significantly. 
For dust control, the benefits of in- 
creasing water pressure above 3,000 psi 
were small. 



FUTURE RECOMMENDATIONS 



The Bureau of Mines is involved in 
planning and conducting the following 
studies on the use of water-jet-assisted 
cutting for longwall mining: 

1. A relationship existed between flu- 
id horsepower (PxV) and dust level for 
all conditions when the sprays were oper- 
ated. Further testing will be conducted 
to study the independent and interactive 



effects of water flow and pressure on 
dust levels. 

2. Water-jet-assisted cutting hard- 
ware, now being developed, will be in- 
stalled on a shearer that will be oper- 
ated on an underground longwall face 
(7^). Airborne respirable dust levels 
will be monitored during normal mining 
operations. 



REFERENCES 



1. Taylor, C. D. , and R. J. Evans 
(comp.). Water- Jet-As sis ted Cutting. 
Proceedings: Bureau of Mines Open Indus- 
try Meeting, Pittsburgh, PA, June 21, 
1984. BuMines IC 9045, 1985, 86 pp. 

2. Hood, M. Water- Jet-Assisted Rock 
Cutting — the Present State of the Art. 
Paper in Water- Jet-Assisted Cutting. 



Proceedings: Bureau of Mines Open Indus- 
try Meeting, Pittsburgh, PA, June 21, 
1984, comp. by CD. Taylor and R. J. 
Evans. BuMines IC 9045, 1985, pp. 3-20. 

3. Morris, A. H. , and M. G. Tomlin. 
Experience With Boom-Type Roadheaders 
Equipped With High-Pressure Water- Jet 
Systems for Roadway Drivage in British 



Coal Mines. Paper in Water- Jet-Assisted 
Cutting. Proceedings: Bureau of Mines 
Open Industry Meeting, Pittsburgh, PA, 
June 21, 1984, comp. by CD. Taylor 
and R. J. Evans. BuMines IC 9045, 1985, 
pp. 29-39. 

4. Kissell, F. N. , N. Jayaraman, C. D. 
Taylor, and R. Jankowski. Reducing Dust 
at Longwall Shearers by Confining the 
Dust Cloud to the Face. BuMines TPR HI, 
1981, 21 pp. 

5. Tomb, T. F., L. Cheng, and R. L. 
Stein. Suppression and Collection of Re- 
spirable Coal Dust Using Water and Steam. 
Paper in Coal Workers' Pneumoconiosis. 



Ann. NY Acad. Sci., v. 200, 1972, 
pp. 724-736. 

6. National Coal Board (London), 
Methods of Reducing Dust Formation and 
Improving Dust Suppression on Longwall 
Faces. Final Rep. on European Coal and 
Steel Community Research Project 7256-12/ 
003/08, 1981, 56 pp. 

7. ETE Corp. Water Jet Assist Cutting 
Evaluation and Cutting Trials. Ongoing 
BuMines contract J0145035. For inf. con- 
tact E. D. Thlmons, TPO, Div. Health and 
Safety, BuMines, Pittsburgh, PA. 



a U.S. GOVERNMENT PRINTING OFFICE; 1986-60501 7/40,038 



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